The present invention relates to a solid-state image pickup device such as a CCD image sensor, a CMOS image sensor or the like, and, particularly, to a pixel defect testing method for testing the solid-state image pickup device for a pixel defect.
Solid-state image pickup devices using a CCD image sensor, a CMOS image sensor or the like have recently been drawing attention as an image input device for various portable terminal apparatuses, digital still cameras, digital video cameras and the like.
A pixel defect can be caused in these solid-state image pickup devices by a local crystal defect of a semiconductor for realizing the solid-state image pickup device, or a dust, stress or the like in a manufacturing process for forming the solid-state image pickup device on a semiconductor.
It is known that such a pixel defect occurring on a solid-state image pickup device results in a white dot, a black dot or the like in an image obtained by the solid-state image pickup device, thus degrading picture quality.
Accordingly, a pixel defect test is performed before shipment of the solid-state image pickup device, for example.
This test uses the same method of reading pixel signals of all pixels as in normal use to pick up an image of a completely black subject at the time of detection of a white dot and pick up an image of a completely white subject at the time of detection of a black dot, for example. When white dots are detected in a completely black image, for example, and a solid-state image pickup device has a certain number of white dots or more or exhibits a certain signal level or more, the solid-state image pickup device is regarded as a defective product, and the solid-state image pickup device is therefore not shipped.
In the meantime, recent solid-state image pickup devices are desired to have more pixels and higher functionality.
Hence, when the number of pixels is further increased, it is expected that an enormous amount of test time will be required with the increase in the number of pixels if solid-state image pickup devices are tested by using the same image pickup operation as in normal use as described above.
For example, a test time required for an SVGA (1280×1024=1.3 million pixels) solid-state image pickup device is about four times that required for a VGA (640×480=0.33 million pixels) solid-state image pickup device.
Further, recent solid-state image pickup devices are desired to have higher functionality, and it is therefore desired that various circuits be mounted on the same semiconductor substrate in addition to a pixel unit. A more complex test process is required for such a solid-state image pickup device.
FIG. 11 shows an example of configuration of a CMOS image sensor.
As shown in FIG. 11, the CMOS image sensor comprises: a pixel unit 110 having a plurality of unit pixels disposed in a two-dimensional arrangement; a driving circuit 111 for driving each pixel of the pixel unit 110; a CDS (correlated double sampling) circuit 112 for removing noise from an output signal (hereinafter referred to as a pixel output signal) from the pixel unit; an amplifier circuit 113 for amplifying the pixel output signal from the CDS circuit 112; an A/D converter circuit 114 for converting the amplified pixel output signal to a digital form; a timing generator 115 for generating an operating pulse for each of the circuits; and the like.
When the CDS circuit 112 is tested, for example, processing is performed such that the pixel unit 110 and the driving circuit 111 are brought into a standby state and a signal is externally inputted to an input part of the CDS circuit 112 to perform the test.
Thus, each of the circuit parts is usually tested in order from a later stage while circuits other than the circuit being tested are in a standby state. This is because of a problem with circuit configuration, in that each part cannot operate independently. In addition, this is also done to increase test analysis accuracy and improve defect coverage, or the probability of defects being found in a test.
For these reasons, it is expected that an enormous amount of test time will be required as the number and complexity of circuits included in a mounted manner are increased with higher functionality.
As described above, with the conventional pixel defect testing method, the test time is expected to be increased further when the solid-state image pickup device has more pixels and higher functionality.
Further, test signals and a test program used for the test become complicated, and therefore it becomes difficult to create and verify test signals and a test program.
Consequently, the burden and cost required for the test are increased.